Electric power system



Dec. 22, 1925.

P. TROMBETTA ELECTRIC POWER SYSTEM Filed March 9, 1924 Z9 Inventor:

par-n ilo Trofn betta,

3/ by fl w/9 His Attorn ey.

Patented Dec. 22, 1925.

UNITED STATES A 1,566,936 PATENT OFFICE.

PANIILO TROIBETTA, OF SCHENEGTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC POWER SYSTEM. I

Application filed March 18, 1924. Serial No. 700,436.

To all whom it may concern:

Be it known that I, PANFILO TROMBETIA, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Electric Power Systems, of which the following is a s cification.

y invention rel-ates to electric power systems, and has for its object the provision of an improved alternating current system wherein power is supplied to a load device, such as the propeller motor of a ship for example, from a plurality of generators driven by independent prime movers.

The Diesel engine has the advantage of high efliciency and for this reason has been extensively used as a means of driving direct current generators connected in series to one or more load motors. This arrangement furnishes ideal condition for the control of the motor torque and speed, and the connection of the generators 1n series permits variation in the speed and torque of the various engines without appreciable efl'ect on the 0 111191011 of the load motor or motors. It is ighly desirable to develop a similar alternatm current system WhlCh retains these g features and at the same time makes it possible to secure the advantages of alternating lcurrent apparatus which,'as compared wit direct current a paratus, is lighter in weight, has higher e enemy, and does not require the use of commutators. Due to its inherent speed characteristics, however, the Diesel engine is unsuited for driving synchronous alternating current generators which are likely to hunt or produce currents which circulate between the various enerators without the production of usefu torque. In accordance with my invention this difiicult is avoided and the advantages of both direct and alternating current apparatus are retained by the use of induction generators driven by prime movers which may have the varying torque charac teristics of internal combustion engines.

My invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the drawing shows a ship pro. ulsion system wherein a double fed propel er motor 1 is arranged to have win 4 respectively through which current is supits stator winding 2 interconnected with a machine group or aggregate comprising inductlon generators 3 and 4 which are arranged be driven by prime movers 5 and 6 respectively and a synchronous machine 7 arranged to be driven by an adjustable speed prime mover such as a steam turbine 8, for example. The synchronous machine 7, wlnch 1s provided for supplying the excitation required by generators 3 and 4 and a part of that reqiuired by the motor 1, is provided wlth a eld windin 9 arranged to be supplied with current tirough leads 10 and a justable rheostat 11. The armature winding 12 of the machine 7 is conductiveliy associated with the series connected mgs 13 and 14 of the generators 3 and plied to the stator winding 2 of the motor 1. The rotor members of the generators 3 and 4 are shown as provided with squirrel cage windlng 15 and 16 respectively. A reversingswltch 17 is provided in the leads through which current is supplied to the motor winding 2.

A machine aggregate similar to the one ust descr bed 1s interconnected with the rotor wind ng 18 of the motor 1 throu h reversmg sw1tch19 and switch 20 which is (also arranged to connect the winding 18 to the adjustable rheostat 21 for urpose ex. plained hereinafter. This mac ine ag eate comprlses generators 22 and 23 driven y prime movers 24 and 25 res etively and provided with armature win ings 26 and 27 interconnected with the armature winding 28 of a synchronous machine 29. The

Assuming the switch 17 to be closed and the switch 20 to be open, the following procedure may be followed in bringing the motor 1 up to speed. The generator 3 may be brought u to a suitable speed, one-half normal speetg for example, and supplied with excitation from the machine 7. The generator 4 will thereupon start as an induction motor and may be driven as a generator I of ed I plied to the winding 2 by supplying fuel 18 to the rheostat 21 which is utilized to accelerate the motor in a manner well known to those skilled in the art.

Assuming that the generators 22 and 23 to have been accelerated as described in connection with generators 3 and 1, and the machine 29 to be supplying exciting current at the low frequency of two or three cycles per second, for example,

the speed of the motor 1 may be further increased by operating the switch 20 to connect the wmdmg 18 to the leads 37 instead of the rheostat 21 and closing the reversing switch 19 in a position to produce through the winding 18 a magnetic field rotating in a directlonopposite to that produced through the win ing 2. It will be apparent that in this method 'rocedure the synchronizing force exerttween the oppositely rotating fields is relied upon to raise the motor speed from a value slightly below to a value slightly above that at which its stator field 1s rotating. If desired this force may be increased by reducing the speed of the machine 7 at the instant that the switch 19 1S closed to supply current to the winding 18. en its rotor and stator fields are instep the speed of the motor may be further increased by bringing the generators 3, 22 and 23 up to full speed and increasing the freuency. of the ,exciting currents supplied by t e machines 7 and 29.

The motor 1 may be brought to rest and started to rotate in the opposite direction by 0 ning the switch 19 operating the switc 20 to connect the winding 18 to the rheostat 21 and reversing the phase rotation of the winding 2 by means of switch 17 to cause the stator field of the motor rotate in a direction the reverse of that in which the winding 18 is driven by the propeller. If desired the frequency of the current supmay be reduced to 1mrove the motor torque characteristics during this stage of the operation. .Under these conditions the motor will come to rest and will accelerate in the reverse direction to a speed de endent upon the frequency of the current elivered by the generators 3 and 4. To increase further the motor speed the winding18 may be connected to the generators 22 and 23 with a phase rotation oppo site to that of the winding 2 and the steps followed in accelerating the motor from rest may be followed. This part of the operation has been described in connection with the operation of starting the motor and will be understood without detailed explanation.

If the stator and rotor fields of the motor 1 be made to rotate in opposite directions as previously indicated it will be apparent that motors ed is directly proportional to the sum of t e frequencies of its stator and rotor currents. The rotor and stator fields may also be caused to rotate in the same direction. When this relation exists the speed of the motor is proportional to the difierence be tween the frequencies of the stator and rotor currents and the motor is at rest when these two fields are rotating at the same rate of speed. This arrangement has the advantage that the frequencies ofthe stator and rotor currents may be made fairly high without requiring an excessive number of poles on the motor to maintain its speed within proper limits. The operation of this arrangem'ent will be readily understood. Assummg the two fields to be rotating at the same speed, the motor may be started from rest in one direction by decreasing the frequency of the rotor current or maybe acoelerated in the opposite direction by decreasin the frequency of the stator current. In eit er case the motor is brought to rest by equalizing the rotational speeds of its rotor and" stator fields.

By combining the induction generator with the Diesel engine certain advantages of both are retained while certain of their ob jectionable features are eliminated. The induction generator, when operated in connection with a s stem having 1ts frequency fixed independent y of the generator, will assume a speed just high enough to supply all the power that it has available. Since the generators will supply to the system as much power as they can without changin its frequency, the question of their speed control becomes a consideration of mmor importance. Therefore, the engines 5 and 6, for example, are independent of each other and their speeds ma vary over a considerable range without a ecting the frequency of the system or overloading the generators. There is thus no tendency for the generators to hunt and the roduction of circulating currents are avoi ed.

While my invention has been illustrated as embodied in a form which now seems preferable, it will be apparent that the synchronous machines will function to supply the excitin current of the induction machines whet er they be connected in series or in parallel therewith.

It will be apparent to those skilled in the art that changes may be made in the embodiment disclosed without departing from my invention. The terms of the appended claims are, accordingly, not restricted to the precise arrangement shownbut are intended to cover all changes and modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electric power system comprising a load device and a machine ag regate for supplying current to said load device, said aggregate including a plurality of series connected induction generators, a plurality of independent internal combustion engines for driving said generators, and means for controlling the frequency of the current delivered by said generators.

2. An electric ship propulsion system comprising a motor having a pair of windings, a machine aggregate for supplying current to one of said windings and a second machine a gregate for supplying current to the other 0% said windings, said aggregates each in- PANFILO TROMBETTA. 

